1. Field of the Invention
The present invention relates to an image forming apparatus configured to transfer a toner image carried on an image carrier to a recording medium by using electro-photographic technology.
2. Description of the Related Art
Hitherto, there is known an image forming apparatus configured to transfer a toner image carried on an rotating endless belt-like intermediate transfer body (referred to as an ‘intermediate transfer belt’ hereinafter) to a recording medium at a transfer nip where the transfer belt is brought into contact with a transfer rotating member, e.g., transfer belt or a transfer roller. A strong electric field is generated at the transfer nip because high voltage is applied to the transfer rotating member to transfer the toner image from the intermediate transfer belt to the recording medium.
By the way, there is a case when the intermediate transfer belt vibrates during its rotation. If the intermediate transfer belt vibrates, a gap can be generated between a toner image carrying surface of the intermediate transfer belt and a recording medium at upstream of the transfer nip (upstream side in the conveying direction of the recording medium). Because the strong electric field is generated at the transfer nip as described above, an abnormal discharge tends to occur between the intermediate transfer belt and the recording medium if the gap is generated at upstream of the transfer nip. If the abnormal discharge occurs, the electrical charge of the toner carried on the intermediate transfer belt is lost and the toner whose electrical charge is lost is not transferred from the intermediate transfer belt to the recording medium. Then, a defective image in which an image of a spot where the abnormal discharge has occurred is omitted (called as a ‘void’ or the like) is generated.
Then, Japanese Patent Application Laid-open No. 2002-82543 discloses a device that suppresses the vibration of the intermediate transfer belt causing the abnormal discharge by disposing a vibration preventing member on a back surface side (side opposite to the toner image carrying surface) of the intermediate transfer belt and by pressing the intermediate transfer belt from the back surface thereof. This arrangement makes it possible to deliver the recording medium to the transfer nip in a state in which the recording medium is adhered to the toner image carrying surface of the intermediate transfer belt without gap at upstream of the transfer nip.
In the image forming apparatus, the recording medium on which the toner image has been transferred is delivered downstream of the transfer nip (downstream in the conveying direction of the recording medium) and is guided to a fixing apparatus in a state in which an opposite side from the surface on which the toner image has been transferred is supported by a conveying belt, a conveying guide, or the like. A direction in which the recording medium is guided is determined in accordance to a position where the fixing apparatus is disposed. For instance, in a case when the fixing apparatus is disposed obliquely upward from a direction in which the recording medium is delivered from the transfer nip, the conveying belt guides the recording medium so as to uplift a front end of the recording medium obliquely upward toward the fixing apparatus.
However, there is a problem in the past that the void caused by the abovementioned abnormal discharge is apt to be generated in guiding a recording medium whose bending rigidity is high such as a thick sheet, a coated sheet or the like. That is, if a ‘stiff’ recording medium is guided in a state in which its front end is uplifted at downstream of the transfer nip, a rear end of the recording medium moves in a direction separating from the intermediate transfer belt at upstream of the transfer nip. Then, the gap is generated between the toner image carrying surface of the intermediate transfer belt and the recording medium, thus causing the abnormal discharge and the void at the spot where the gap is generated.